How do I remove two consecutive same characters from a string?

Question

I am trying to remove consecutively same characters from a string. For example:

         abb --> ab
         aaab --> ab
         ababa --> ababa (since no two consecutive characters are same)

My code:

T=int(input())
l=[0]
S1=""
for i in range(T):
    S=input()
    for j in range(len(S)-1):
        if S[j]!=S[j+1]:
            if S[j] != l[len(l)-1]:
                l=[]
                l.append(S[j])
                l.append(S[j+1])
                print(l)

            for k in l:
                S1+=k
            

    print(S1)
    S1=""
    l=[0]

The code doesn't work for the third case (ababa). How do I fix this?

Does this answer your question? [How to remove duplicates only if consecutive in a string?](https://stackoverflow.com/questions/11460855/how-to-remove-duplicates-only-if-consecutive-in-a-string) — Tomerikoo, Dec 06 '20 at 13:36
Shouldn't `aaab` become `aab`? It has only once 2 consecutive `a`s... — Tomerikoo, Dec 06 '20 at 14:02

user2390182 · Answer 1 · 2020-12-06T13:24:39.190

2

One concise approach would use itertools.groupby:

from itertools import groupby

def clean(s):
    return ''.join(k for k, _ in groupby(s))

>>> clean("abb")
'ab'
>>> clean("aaab")
'ab'
>>> clean("ababa")
'ababa'

A rather simplified quadratic loop-based approach (linear in comments):

def clean(s):
    res = ""  # res = []
    for c in s:
        if not res or res[-1] != c:
            res += c  # res.append(c)
    return res  # return ''.join(res)

edited Dec 06 '20 at 13:24

answered Dec 06 '20 at 13:18

user2390182

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According to the described desired output, it should become `ab` – user2390182 Dec 06 '20 at 13:22
Q sounds like a homework assignment. I wonder if hiding so much of the problem behind `groupby` is going to fly. – CryptoFool Dec 06 '20 at 13:24

score 1 · Answer 2 · answered Dec 06 '20 at 13:25

1

A verbose way of doing it, may not be most efficient if the strings are large:

value = 'aaaaaabbbbaaaaaacdeeeeefff'

def no_dups(value):
    r = ''
    for i in value:
        if not r or r[-1] != i:
            r += i
    return r

print(no_dups(value))
# abacdef

answered Dec 06 '20 at 13:25

Sazzy

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It just drop duplicates not only the connsecutive ones – Hamza Dec 06 '20 at 13:26
@Hamza - I don't see that. His example looks right. Can you provide an input for which this fails? – CryptoFool Dec 06 '20 at 13:29

score 1 · Answer 3 · answered Dec 06 '20 at 13:28

1

Using regex, we could do re.sub(r'([a-z])\1+', r'\1', string_data)

import re

test_data = 'abb aaab ababa'.split()

for data in test_data:
    print(f"{data} -->", re.sub(r'([a-z])\1+', r'\1', data))

answered Dec 06 '20 at 13:28

Prayson W. Daniel

14,191
4
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That is very similar. Yes! – Prayson W. Daniel Dec 06 '20 at 14:11

score 1 · Answer 4 · answered Dec 06 '20 at 13:29

Came out with this code, works properly:

T=int(input())      #No of testcases; for testing multiple strings
S1=""
for i in range(T):
    S=input()
    for j in range(0,len(S),2):
        if j!=len(S)-1:
            if S[j]!=S[j+1]:
                S1+=S[j]
                S1+=S[j+1]
        else:
            if S1[len(S1)-1]!=S[j]:
                S1+=S[j]

    print(S1)
    S1=""

Hamza · Answer 5 · 2020-12-06T13:48:44.297

1

You can use regex as:

for char in set(string):
    string = re.sub(f'{char}+', char, string)
string

results in

 abb --> ab
 aaab --> ab
 ababa --> ababa

edited Dec 06 '20 at 13:48

answered Dec 06 '20 at 13:36

Hamza

5,373
3
28
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Indeed thats right! I will make it more efficient! – Hamza Dec 06 '20 at 13:40

How do I remove two consecutive same characters from a string?

5 Answers5